Secure communication systems of today are nearly impenetrable to an adversary. Since most successful encryptions used in conjunction with secure systems are based on extremely long pseudo-random sequences that take millions of years to repeat themselves, an encrypted transmission sounds like noise to a listener who does not have the appropriate receiving and decrypting equipment.
Secure transmissions are encrypted with a key, which, as is well-known in the art, is a relatively lengthy number that is used by an encryption device to generate a key stream. The key stream is combined with the information desired to be encrypted (known as plain text in the art) to produce an encrypted data stream known as cipher text.
The part to whom the encrypted message is directed is equipped with a decryption device that will successfully decrypt the transmitted message only if the decryptor is equipped with the same key that was used to encrypt the message. Thus, loss of the encryption key at either the transmitting or receiving end will render the secure communication system useless.
Encryption keys are normally stored in memory devices that require a constant power source in order to preserve memory integrity. With fixed equipment installations, that is, equipment designed to remain in one place for relatively long periods, a main power source derived from the A.C. (alternating current) distribution network can be used to provide power to memory devices.
Of course, power fluctuations, and even total failures, occur with regularity. Therefore, some kind of back up power supply is required in order to preserve encryption keys should partial or total failure of A.C. power come to pass.
At odds with the requirement for preserving encryption keys is the necessity for keeping knowledge of the keys out of the hands of an adversary. If main power were to fail, a battery backup system would eventually begin to degrade. The voltage available from the backup supply may even decay to the point where it is no longer possible to successfully erase an associated key store.
Accordingly, a need arises for a method for backing up an encryption key memory while still ensuring that critical key variables can be erased if necessary.